As the art regarding the polyamino oligomers of this invention, there is known a process for preparing bis(p-aminocumyl)benzenes through acid catalytic reaction of aniline derivatives and diisopropenylbenzenes.
For instance, in German Patent No. 2,111,194, U.S. Pat. No. 3,365,347 and Japanese Patent Application Kokai No. 44/1986, it is proposed to react aniline derivatives and diisopropenylbenzenes under the appropriate conditions by using an acid catalyst and further carry out a purification operation such as crystallization for obtaining pure bis(p-aminocumyl)benzenes.
Bis(p-aminocumyl)benzenes obtained according to these methods are a crystalline solid with a melting point of 100.degree. C. or higher, so that when they are blended in a resin, it is necessary to apply a pertinent treatment such as heating them to a temperature higher than their melting point or dissolving them in a suitable solvent. These treatments, however, would give rise to such problems as increase of viscosity of the resin due to the advancement of reaction and formation of voids in the course of curing reaction, so that a compound which unnecessitates these treatments has been desired.
The polymaleimide compounds are being made practical use of by utilizing their excellent heat resistance, but they have the defects that they singly are hard to dissolve in general-purpose organic solvents and are also low in water absorptivity and poor in electrical properties due to their high polarity.
For overcoming these defects, bis(p-aminocumyl)benzenes obtained from an acid catalytic reaction of aniline derivatives and diisopropenylbenzenes, such as mentioned above, are further reacted with maleic anhydride in the presence of a dehydrating agent, a catalyst and a base to obtain bis(p-N-maleimidecumyl)benzenes, as described in International Application Laid-Open No. W087/00835. However, these compounds, being a crystalline solid with a high melting point, need to be subjected to a pertinent treatment such as melting by heating to a temperature above their melting point or dissolving in a suitable solvent, before molding. In the former case, since the difference between the compound melting point and the maleimide group reaction temperature is reduced, the time available for molding might be limited, and in the latter case, there is a risk of causing formation of voids in the course of molding. Also, these compounds are not necessarily satisfactory in water resistance and electrical properties.
Thermosetting resins have been popularly used as matrix resin for printed wiring boards. With operational speedup of semiconductor elements in multi-layer printed wiring boards for high-speed computers in recent years, necessity is increasing for corresponding speedup of response of circuitries on the printed board. Signal propagation speed in circuitries on the printed board depends on dielectric constant of the insulating material holding the circuitries, and generally the lower the dielectric constant of a material, the higher signal propagation speed it offers. Hitherto, polyimide resins and heat resistant epoxy resins have been used for such purpose.
The conventional polyimide resins and heat resistant epoxy resins indeed have excellent heat resistance, but the dielectric constant of these resins as a single body is as high as 3.4 to 3.9, and the laminate made by combining such resin with E-glass cloth has even a higher order of dielectric constant, 4.5 to 5.0. For reducing dielectric constant of the laminates to less than 4.0, it was proposed to modify the resin with a pertinent substance such as polybutadiene, but this method involves the problem that heat resistance of resin is lowered, and for this reason, it has not been applied to practical use. Thus, a resin composition capable of forming a laminate with a dielectric constant of 4.0 or less without impairing heat resistance has been strongly desired.
In order to solve the above problem, it is necessary to prepare a resin composition using a polymaleimide compound derived from a polyamino compound into which a novel molecular structure having the effect of improving water resistance and electrical properties has been introduced, said resin compositions having a low melting point (softening point) and capable of use without a solvent for the improvement of moldability, and to apply such a resin composition as matrix resin for the laminates.